For R2, we compute political diversity using Shannon's entropy and infer the political ideology of each account \(p\)  follows using a state-of-the-art classifier presented in [1]}. R3 is measured using political alignment scores inferred as a part of [2]} for different web domains. The results section provides additional details on each of these outcome variables and how they are computed. We can think of these response variables as seeking to measure changes in what participants “believe” (R1), who they “listen” to (R2), and what they “speak” about (R3) on Twitter — all of which help to illuminate the nature of political echo chambers on social media.
